Geochemical characteristics and tectonic implications of the Neoproterozoic A-type granites in Red Sea State, Sudan
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摘要: 苏丹红海州位于努比亚地盾，本文在该地厘定出一套新元古代花岗岩，由中粗粒-中细粒正长花岗岩、中细粒碱长花岗岩组成，LA-ICP-MS 定年结果显示，岩体形成于713±4 Ma，属于泛非造山事件的产物。花岗岩SiO2含量较高，为70.80%～77.83%，A/CNK 为0.94～1.08，A/NK 为1.12～1.44，为准铝质-弱过铝质花岗岩。花岗岩具有相似的稀土元素和微量元素配分模式，稀土配分模式呈右倾V 字形曲线，轻重稀土分异中等（LREE/HREE=2.46～7.13），δEu为0.30～0.57，负铕异常中等-强烈。富含大离子亲石元素Th、U、K和高场强元素Zr、Hf，亏损高场强元素Nb、Ta、Sr、P和Ti。花岗岩具有低ISr比值、亏损εNd(t)值和εHf(t)值，TDM1与TDM2值较为一致。岩体为A2型花岗岩，形成于俯冲阶段弧后拉张环境，因弧后伸展减薄导致软流圈物质上涌，明显的升温、减压促使新生地壳部分熔融。Abstract: The Red Sea State of Sudan is located in the Nubian shield.A series of Neoproterozoic granites are identified in the Red Sea State, which consist of medium-coarse-and medium-fine-grained syenogranites and middle-fine-grained alkli feldspar granites.Zircon U-Pb dating implies the granites are intruded in 713 ±4 Ma, which are formed in Pan-African orogenic event.They show high SiO2 contents (70.80%~77.83%).They are metaluminous or weak peraluminous with A/CNK ratios of 0.94~1.08 and A/NK ratios of 1.12~1.44.They show the similar Chondrite-normalized REE and multi-trace elements patterns.The REE patterns are rightinclined with REE medium differentiations of LREE/HREE ratios of 2.46~7.13 and display“V”shaped curve and medium to strong Eu anomaly with δEu values of 0.30~0.57.The granites are characterized by the enrichment of large ion lithophile elements (LILEs) such as Th, U, K and high field-strength elements (HFSEs)such as Zr, Hf and by the depleted Nb, Ta, Sr, P and Ti contents.They show low ISr ratios, depleted εNd(t), εHf(t)values and the similar TDM1 and TDM2 values.The granites chemically show A2-type affinity.We propose that the 713 Ma A-type magmatism might be driven by upwelling of asthenosphere and subsequent partial melts of juvenile crust of Nubian shield on conditions of obvious Heating and decompression in a back-arc extensional setting.
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